Analysis of sulfamethazine in milk by an immunosensor assay based on surface plasmon resonance

A recently developed immunosensor assay was applied in the analysis of sulfamethazine residues in milk from individual cows, herds and car tankers. Previously frozen milk samples were defatted by centrifugation whereas fresh milk required no sample preparations. The average relative standard deviation and the limit of detection of the assay were less than 2% and 1 mu g/kg, respectively. The correlation with a conventional HPLC method was found to be high in analysis of incurred samples from a sulfamethazine-treated cow. In addition, the method was used to analyse 330 tanker milk samples, of which one was found to contain sulfamethazine at the low ppb level by both the immunosensor assay and HPLC.